Mike,
I did pull down your repo and ran some tests.
This version of k-nucleotide does run faster than the currently submitted version in alioth.
However, we've got a ways to go to catch the faster Java implementations.

I've added a few comments in your repo.
Of note, the (set! unchecked-math true) directive at the top of files allows us to use inc, dec, etc directly without explicitly specifying unchecked-inc, etc.